合并二叉树

解题思路：将两个节点的值求和并赋给t1，然后递归合并t1、t2的左右节点。

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param t1 TreeNode类 
     * @param t2 TreeNode类 
     * @return TreeNode类
     */
    public TreeNode mergeTrees (TreeNode t1, TreeNode t2) {
        // write code here
        t1.val=t1.val+t2.val;
        if(t1.left!=null&&t2.left!=null){
            mergeTrees(t1.left,t2.left);
        }
        else if(t1.left==null&&t2.left!=null){
            t1.left=t2.left;
        }
        if(t1.right!=null&&t2.right!=null){
            mergeTrees(t1.right,t2.right);
        }
        else if(t1.right==null&&t2.right!=null){
            t1.right=t2.right;
        }
        return t1;
    }
}